I'm sure when I was ticking boxes on my insurance it specifically asked about performance modifications.Any deviation away from the specification of the vehicle when it left the factory is classed as a modification.
If you're talking about any difference since it left the factory, I would hazard a guess that 99% of peoples cars on here are technically modified in some way.
I mean, are you using OEM brake pads, the exact model and make or tyre that came with it. Have you added mats, de-tangoed indicators?